Anything explicitly discriminatory that the government could have done something about and chose not to. We need to forget about "microaggressions" and deal with the macroaggressions. It's typical that white liberals have embarked on the project of detecting subtle clues to the slightest slights and condemning people for them, when they should just treat historical race-based abuse claims like any other compensation claim.

If you look at black people's family trees enough, you'll find plenty with specific inheritance claims against their white, slaver ancestors. Black people in America are the descendants of white rapists as well as imported slaves.